How would HUD even work since your eyes need to focus on elements between far and close? Would you need to focus on the HUD? Does glasses work the same way? Could some nerd with glasses explain how do you focus on things?

I don't focus on the glasses lens, I focus on whatever object I'm looking at, the light reflected from which is modified by the structure of the lens.

HUD I don't know about, but can tell you, focusing on something an inch in infront of your eye is near impossible, so whatever a HUD does it must project like the image is at a distance. Probably works great for people with good eyesight already, but us aging geeks may require some adjustment as the old eyes don't want to focus up close like they once did.